Method and system to improve handover between mobile video networks and cells

ABSTRACT

A digital video broadcast network comprises a content provider and several transmitters. Each transmitter may transmit more than one signal, different signals having different frequencies, multiplexes and the like and relating to different network types. An integrated receiver/decoder (IRD) is mobile in the area around the transmitters. As well as transmitting service information as part of a network information table on a data layer, the transmitters provide in their output signals transmitter parameter information as TPS data on a physical layer. This TPS information includes information identifying whether there are other networks available, and preferably the number of other networks. Transmission parameters relating to the other networks are included in an other_network_descriptor, forming part of an NIT actual or a BAT, or alternatively in an NIT_other. This information is used by the IRD in signal scan. Using the described broadcast signals, signal scan can be made more efficient, resulting in reduced power consumption and scanning time. IRDs may also receive free field three dimensional models of signal levels created for a group of cells. The models may be in the form of bitmaps and used during handover procedures.

The present application claims priority to GB application 0412871.6filed in Great Britain on Jun. 9, 2004 and to U.S. provisionalapplication Ser. No. 60/548,735 filed on Feb. 27, 2004. The entiredisclosures of both applications are hereby incorporated by reference.

FIELD OF THE INVENTION

Aspects of the invention relate to network and cell handover proceduresin wireless communications systems. More particularly, aspects of theinvention use transmission parameter information for nearby networks andmodels of cells that map quantized signal levels into pixels within thecell coverage area when making handover decisions.

DESCRIPTION OF THE RELATED ART

Digital broadcasting systems, such as various DVB-T (Terrestrial DigitalVideo Broadcasting) and DAB (Digital Audio Broadcasting) systems, ATSC,ISDB and other similar broadcasting systems allow for a systemcomprising transmitters arranged in a cellular fashion, allowing signalreception of a suitable quality over a geographical area throughsuitable transmitter site selection. The cellular nature of thetransmitters' coverage allows mobile receivers to be able to achievesatisfactory performance even when moving. Steps are being taken toincorporate DVB receivers into mobile telephones and Personal DigitalAssistants (PDAs), for which applications the DVB standards were notprimarily designed. Steps are also being taken to provide services overDVB transmissions. A user may buy services using, for example, thetelephone or other bidirectional data transceiver forming part of themobile telephone or PDA.

A receiver, on decoding the transmission parameter information like theTransmission Parameter Signalling (TPS) data in DVB for a receivedsignal, can use it in certain decision making processes. In particular,a DVB-T receiver in a mobile device can use the cell identificationinformation to eliminate some candidate signals in a handover procedure.

A form of DVB is being tailored for use in mobile receiver environments.This is known as DVB handheld, or DVB-H. In DVB-H, Internet Protocoldatacast (IPDC) services are time-sliced, resulting in data for aservice being transmitted over a relatively short period of time withrelatively high bandwidth. A mobile receiver then needs to receive dataonly during this short period of time, and its receiver can be switchedoff at other times. This has positive implications for power consumptionin the mobile receiver. Time-slicing is not limited to DVB-H.

In DVB-T or DVB-H, a receiver needs to perform signal scan, inparticular on power-up for initialising the receiver with existingnetworks within the current location. Moreover, the signal scanoperation needs to be performed periodically if the receiver moves longdistances, and also when the network structure changes. Signal scan cantake a considerable amount of time, often up to five minutes dependingon the network configuration and the availability of signals andnetworks.

While traveling within a network, handover decisions for mobileterminals are typically made based on factors such as cell coverage,mobile terminal location and terminal movement information. With a firstconventional approach, handover decisions are based on location, cellcoverage area and terminal movement vector information. Cell strengthsare conventionally modeled by assuming that cells provide the samesignal strength within square areas. Such modeling methods areinaccurate and can lead to less than optimal handover decisions.

With a second conventional approach to handover decisions between cells,handover decisions are made based on a location determination that is afunction of signal strength, measurement information and cell coverageinformation. With this approach, a mobile terminal is not aware of itslocation (e.g. doesn't have GPS) but is able to measure the signalstrengths of the surrounding cells. In this case a mobile terminal canroughly detect its position by means of cell area coverage informationand signal strength values of surrounding cells. One skilled in the artwill appreciate that location information obtained by measuring signalstrengths is not precise and can lead to less than optimal handoverdecisions.

Therefore, there is a need in the art for procedures and systems thatutilize parameter information broadcast by a first network and thatdescribe characteristics of other networks to optimize handover betweennetworks. There is also a need in the art for handover procedures andsystems that use accurate models of cell station signal strengths tooptimize handover procedures between cells.

BRIEF SUMMARY OF THE INVENTION

One or more of the above-mentioned needs in the art are satisfied by thedisclosed methods and systems.

According to a first aspect of the invention, there is provided a methodof operating a receiver, the method comprising: receiving a signaldigitally broadcast from a transmitter of a prevailing network, thesignal including transmission parameter information bits; decoding thetransmission parameter information from the received signal; anddetermining from the decoded transmission parameter information whetheror not one or more other networks are available.

According to a second aspect of the invention, there is provided areceiver comprising: a receiver arranged for receiving a signaldigitally broadcast from a transmitter of a prevailing network, thesignal including transmission parameter information bits; a decoder fordecoding the transmission parameter information from the signal; and adeterminer for determining from the decoded transmission parameterinformation whether or not other networks are available.

These aspects of the invention can allow improved receiver operation, inparticular by allowing the receiver to determine from the transmissionparameter information bits broadcast in respect of one network whetheror not there are or could be other networks. This may be particularlyimportant when performing signal scan, for initializing a receiver withparameters needed for service discovery. Should the receiver becontrolled to accept this information as valid, it can allow asignificantly simplified network signal search. This may be particularlyimportant in a mobile receiver, since signal search can be timeconsuming, introducing the possibility of error in a moving receiverenvironment, and also involve undesirable power consumption. Theinvention can allow these disadvantages to be ameliorated. In systemssuch as the DVB system, this is particularly advantageous since theservice information, in a worst case scenario, may be transmitted onlyonce in a ten second interval, whereas the transmission parameterinformation may be available very quickly after achieving lock to thetuned signal. The TPS is defined over 68 consecutive OFDM symbols,referred to as one OFDM frame. Four consecutive frames correspond to oneOFDM super-frame. The reference sequence corresponding to the TPScarriers of the first symbol of each OFDM frame are used to initializethe TPS modulation on each TPS carrier. Each OFDM symbol conveys one TPSbit. Each TPS block (corresponding to one OFDM frame) contains 68 bits.The inter-bit interval of TPS bits depends on the symbol speed of thesignal. Typically all the TPS bits are received within 100 ms or less.

In DVB-T and DVB-H, transmission parameter information is transmitted ona lower level than service information. In the embodiments, serviceinformation is transmitted on a data level (OSI level 2) whereas TPSinformation is transmitted on a physical level (OSI level 1). The term‘level’ will be understood to mean a layer in a protocol stack, such asbut not limited to the OSI seven layer model.

According to a third aspect of the invention there is provided a methodof operating a receiver, the method comprising: receiving a signaldigitally broadcast from a transmitter of a prevailing network, thesignal including other network descriptor information; decoding theother network descriptor information from the signal, obtaining from theother network descriptor information transmission parameters relating toone or more other networks, and using the transmission parameters totune the receiver to the one or more other networks.

According to a fourth aspect of the invention there is provided areceiver comprising: a receiver arranged for receiving a signaldigitally broadcast from a transmitter of a prevailing network, thesignal including other network descriptor information; a decoder fordecoding the other network descriptor information from the signal, meansfor obtaining from the decoded other network descriptor informationtransmission parameters relating to one or more other networks, and atuner controller arranged for using the transmission parameters to tunethe receiver to the one or more other networks.

These aspects of the invention can allow improved receiver operation, inparticular by allowing the receiver to determine from the other networkdescriptor information broadcast in respect of one network transmissionparameters relating to one or more other networks. This may besignificant since, should the receiver be controlled to accept thisinformation as valid, it can allow a significantly simplified networksignal search. This is particularly important in a mobile receiver,since signal search can be time consuming, introducing the possibilityof error in a moving receiver environment, and also involve undesirablepower consumption. The invention can allow these disadvantages to beameliorated.

According to a fifth aspect of the invention there are provided systemsthat use free field three dimensional models of signal levels createdfor a group of cells. The models may be in the form of bitmaps. A mobileterminal can determine the inner area within the cell where it islocated, based on the measured signal strength and maximum signalstrength value (depending on the antenna sensitivity of the receiver andcalibrated ‘free-field’ signal strength) indicated in the bitmapinformation. This information may be used to execute handoverprocedures. In various implementations, a mobile terminal can determinethe inner area within the cell where it is located, based on themeasured signal strength and maximum signal strength value (depending onthe antenna sensitivity of the receiver and calibrated ‘free-field’signal strength) indicated in the bitmap information. In one particularimplementation, a mobile terminal is provided and configured to usebitmap information to improve handover procedures.

In other aspects of the invention, computer-executable instructions forimplementing the disclosed methods are stored on computer-readablemedia.

One skilled in the art will appreciate that one or more of the aspectsof the invention described above may be combined. For example, variousaspects of the invention may utilize one or more of the disclosednetwork handover procedures in combination with one or more of thedisclosed cell handover procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitedin the accompanying figures in which like reference numerals indicatesimilar elements and in which:

FIG. 1 is a schematic drawing of a digital video broadcast system,including components operating according to an embodiment of theinvention;

FIG. 2 is a schematic drawing of one of the transmitter stations of thesystem of FIG. 1;

FIG. 3 is a schematic drawing of an integrated receiver/decoder of thesystem of FIG. 1;

FIG. 4 is a flowchart illustrating operation of the integratedreceiver/decoder of FIG. 3 in a signal scan procedure when broadcastdata is according to a first embodiment of the invention;

FIG. 5 is a flowchart illustrating operation of the integratedreceiver/decoder of FIG. 3 in a signal scan procedure when broadcastdata is according to a second embodiment of the invention;

FIG. 6 illustrates the mapping of signal coverage area into a bitmap, inaccordance with an embodiment of the invention;

FIG. 7 illustrates the mapping of a non-uniform signal coverage areainto a bitmap, in accordance with an embodiment of the invention;

FIG. 8 illustrates an exemplary method for generating bitmaps, inaccordance with an embodiment of the invention;

FIG. 9 illustrates an exemplary method for parsing and utilizing asignaling item containing bitmap information in accordance with anembodiment of the invention;

FIG. 10 illustrates a system for creating a data file that containsbitmap information, in accordance with an embodiment of the invention;

FIG. 11 illustrates a system for receiving a data file, creating aCDT-table and broadcasting the CDT-table to mobile terminals, inaccordance with an embodiment of the invention;

FIG. 12 illustrates an exemplary data structure for expressing vectorinformation, in accordance with an embodiment of the invention;

FIG. 13 illustrates a vector that represents movement of a mobileterminal relative to two cells, in accordance with an embodiment of theinvention; and

FIG. 14 illustrates an exemplary method for executing a handoverdecision between networks and cells, in accordance with an embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

I. Handover Between Networks

The standards document EN 300 744 V1.5.1 published by the EuropeanTelecommunications Standards Institute (ETSI) specifies TPS carriers,which are used for signalling parameters related to the transmissionscheme used. The TPS carriers are constituted at a physical layer, orOSI layer 1, of the communication protocol stack. The decoding of theTPS in a receiver allows the channel coding and modulation used in thetransmission to be determined, which information is used in controllingthe receiver to operate accordingly. The TPS data is defined over 68consecutive OFDM (Orthogonal Frequency Division Multiplex) symbols,referred to as one OFDM Frame. The TPS data is transmitted in parallelon seventeen TPS carriers for the DVB 2K mode, on 34 carriers for the 4Kmode, and on 68 carriers for the 8K mode. Every TPS carrier in the samesymbol conveys the same differentially encoded information bit. The TPSis transmitted as shown in Table 1. TABLE 1 Bit Numbers Purpose/contentS₀ Initiation S₁-S₁₆ Synchronisation Word S₁₇-S₂₂ TPS length indicatorS₂₃-S₂₄ Frame Number (in a Super-Frame) S₂₅, S₂₆ Constellation (QPSK or16 or 64 QAM) S₂₇, S₂₈, S₂₉ Hierarchy Information S₃₀, S₃₁, S₃₂ Coderate, HP stream S₃₃, S₃₄, S₃₅ Code rate, LP stream S₃₆, S₃₇ GuardInterval S₃₈, S₃₉ Transmission Mode (2K, 4K or 8K) S₄₀-S₄₇ Cellidentifier S₄₈, S₄₉ DVB-H signalling S₅₀-S₅₃ Reserved for future useS₅₄-S₆₇ Error protection (BCH code)

It should be noted that the synchronisation word takes one value for oddnumbered frames and the inverse for even numbered frames in aSuper-Frame. Also, the cell identifier is two bytes long, and is dividedbetween successive Frames.

More important to some decision-making processes is the informationreceived as service information (SI), which is described in detail inDVB standards document ETS 300 468. The standard document ISO/IEC13818-1 specifies Program Specific Information (PSI). The PSI/SI dataprovides information for enabling automatic configuration of a receiverto demultiplex and decode the various streams of programs within themultiplex signal. The PSI/SI data includes a Network Information Table(NIT), which provides information relating to the physical organisationof the multiplexes, also known as Transport Streams (TS), carried via agiven network. A receiver can store the NIT contents, to minimise accesstime when switching between channels. The PSI/SI data forms part of thedata layer, or OSI layer 2, of the communication protocol stack.

A receiver, also known as an Integrated Receiver/Decoder (IRD) detectsparameters of a prevailing signal and/or network by filtering andparsing a received PSI/SI table. From this information, an IRD candetermine whether or not a signal is a valid handover candidate.However, since typically PSI/SI tables may be transmitted in anyinterval from 25 milliseconds to 10 seconds, depending on the table(e.g. maximum interval for NIT table is 10 seconds), and since thePSI/SI information is transmitted on a data layer (i.e. OSI level 2),signal scanning and handover processes can be expected to involveutilisation of a significant amount of the processing, receiver andpower resources of the IRD, as well as being time consuming. This is ofparticular importance as regards power consumption in battery-operatedmobile handheld devices.

Referring firstly to FIG. 1, an example of a Terrestrial digital videobroadcasting (DVB-T/H) system is shown generally at 1. The systemcomprises a content provider 2, which is connected by suitable links toeach of first, second and third transmitter stations 3, 4, 5. Thetransmitter stations 3-5 are separated from each other at locationsselected such as to provide suitable coverage of the surroundinggeography. In FIG. 1, the transmitters 3-5 are shown having respectivecoverage areas 3 a, 4 a and 5 a, although it will be appreciated that inpractice the area covered by a given transmitter will not be so regularand that there will be significant amount of overlap between thecoverage areas 3 a-5 a. Also shown in FIG. 1 are first and secondintegrated receiver/decoders (IRD) 6, 7. The content provider 2 hasaccess to sources of content 8 a, 8 b, such as audio-visual content,data files or images. The content is transmitted using IP over DVB-Tnetwork, in what is known as an IP Datacasting (IPDC) service, andpreferably using time-slicing, to one or more of the IRDs 6, 7, whichare configured to receive data from one or more different communicationchannels. The IRDs 6, 7 in this embodiment are mobile devices that maybe incorporated in mobile telephones or personal digital assistants(PDA), for example.

The content data is transmitted to a network element 9, which in thisexample is a server configured to receive the content data and togenerate recovery data for use in forward error correction of thecontent data. The content data is transmitted to the IRDs 6, 7 via thetransmitters 3-5. The recovery data is transmitted to the IRDs in oneembodiment of the invention via a second communication channel providedfor example by a Third Generation (3G) mobile network (not shown). Itshould be noted that the communication paths for the content andrecovery data are described with reference to and shown in FIG. 1 in asimplified form. However, other elements such as further transmitters,network elements or networks may be situated in these communicationpaths

Each IRD 6, 7 is able to receive and decode signals transmitted by anyor all of the transmitters 3-5.

Each of the transmitters 3-5 is substantially the same, and one isillustrated in FIG. 2. Referring to FIG. 2, a transmitter station 3 isshown in schematic form, comprising generally a data source in the formof a combiner 10, a transmitter 11 and an antenna 12. The combiner 10receives input data from a content provider 13, which is connected viaan input 14 to the content provider 2 shown in FIG. 1. Also arranged toprovide data to the combiner is a Program Specific Information (PSI) (orService Information (SI)) data generator 15. The transmitter 11 includesa transmission parameter signalling (TPS) data generating device 16. Thecombiner 10 is arranged to source data from the content provider device13 and the PSI/SI generator device 15 and to provide a data streamaccording to the DVB standards for inclusion with TPS data andsubsequent transmission by the transmitter 11. According to the EN 300744 standard, data provided by the TPS generator 16 is included in thephysical layer of the transmitted signals many times a second, whereasthe PSI/SI generating device 15 data is included in the data layer ofthe transmitted signal and much less frequently, with up to 10 secondintervals between data transmissions. As is conventional the PSI/SIgenerator 15 generates data representing a network information table(NIT), which is in accordance with the DVB standards. The transmitter 11can therefore be considered to include transmission parameterinformation provided by the TPS generator 16 with service informationprovided as part of the data generated by the PSI/SI generator 15. Theresultant signal can be considered as a composite signal, and it is thecomposite signal which is then transmitted by the transmitter 11 by wayof the antenna 12. Of course, the composite signal also includes contentdata provided by the content generator 13, and other data which isoutside the scope of this disclosure.

Each of the transmitters 3-5 may transmit plural signals according tothe DVB standards. In this connection, the transmitters 3-5 may includeplural physical transmitters at a single location and sharing a commonantenna. Each signal transmitted by a given one of the transmitters 3-5may differ from other signals in terms of the frequency of the signal,the network type, the format of the transport stream, the network'stopology, the transmitter power, and the nature of the multiplexingused. For example, multiplexing may be in a time-sliced nature, which isconceptually similar to time division multiplexing, or it may be thatmultiplexing is effected other than in the time domain. The types oftransport stream which might be used will be known by those skilled inthe art. The network type might be, for example, a DVB-T/H network or anInternet Protocol Data Cast (IPDC) network. The topology of the networkmight be single frequency or multiple frequency. A multiple frequencynetwork might have transmissions on plural contiguous frequency bands.The present DVB standards allow for bandwidths of 5, 6, 7 and 8 MHz. Theimplementation of DVB-T in Europe is presently utilising signals havinga bandwidth of 8 MHz.

The TPS data transmitted by the transmitter 11 via the antenna 12differs from conventional TPS data by the inclusion of additionalinformation therein.

The IRD 6, 7 will now be described with reference to FIG. 3. Referringto FIG. 3, the IRD 6, is shown very schematically, comprising generallya central processing unit (CPU) 20, which is connected to control eachof a primary decoder 21, a receiver 22, a secondary decoder, e.g. anMPEG-2 and IP (Internet Protocol) decoder 23, to storage means such as anon-volatile flash memory 27, and to a volatile SDRAM memory 28.

The receiver 22 is connected to receive radio frequency signals via anantenna 24, and to provide demodulated signals to the decoder 21. Theprimary decoder 21 is arranged under control of the CPU 20 to providedecoded data both to the CPU and to provide MPEG or IP data to thesecondary decoder 23. The secondary decoder 23 provides audio outputs toa speaker 25 and visual outputs to a display 26, whereby audiovisualcontent present in the signal received at the receiver 22 can bepresented to a user. Although in this example IP and MPEG signals areable to be processed by a common decoder 23, it will be appreciated thatseparate decoders could be used instead.

The flash memory 27 may be used to store data parsed from an NIT duringsignal scan. The SDRAM 28 may be used to store some of the data used inearlier stages of a handover procedure.

Although not essential, the IRD 6 also may include a transceiver 29 forallowing communication in a mobile telephone system, such as e.g. GSM,GPRS, 3G, UMTS for example, which is coupled to a corresponding mobiletelephone and data handling module 30. The transceiver 29 and the module30 allow the IRD 6 to operate as a telephone and mobile Internet portal,as well as to allow the user of the IRD to subscribe to services ofinterest which are communicated by data cast using the DVB network. Thiscan be achieved in any convenient manner. For example, the user mightsend a request for service delivery to a mobile telephone operator withwhich the user subscribes using the UMTS components 29, 30. The operatormay then arrange for the service to be provided via DVB using anInternet service provider. Notifications of service delivery may becommunicated to the IRD using the UMTS system or the DVB system.

The IRD 6 differs from conventional IRDs in that it is arranged todetect information relating to other network and forming part of TPSdata, and to utilise that data appropriately. Operation of the IRD 6 ina signal scan procedure will now be described with reference to FIG. 4.It will be understood that the signal scan procedure is performed forinitialising the receiver 6 with parameters needed for OSI layers 1 and2 service discovery and for subsequently updating these parameters.

The first embodiment, which will now be described with reference toFIGS. 1 to 4, can allow more rapid discovery of other signals, using TPSbits and a descriptor called ‘other_network_descriptor’. More rapiddiscovery typically decreases power consumption during signal scanning(i.e. initialization). The described ‘other_network_descriptor’ can alsobe used by a receiver to determine when it should update its database,by performing signal scan.

Briefly, the TPS bits include an indication of whether other networksare available or not, and information concerning the available signalsof other networks is signaled using the other_network_descriptor. Thisdescriptor can be included for example in the NIT, or alternatively inthe BAT (Bouquet Association Table). A receiver is able to detect theavailability of other networks from the TPS bits transmitted in respectof one signal or network. The receiver can also determine informationconcerning these other networks using information included in theother_network_descriptor. An NIT is segmented into sections describingthe _actual network and _other networks. There are two table ids usedfor NIT sections, 0x40 for sections describing the _actual network and0x41 for sections describing _other networks.

Each network comprises one or more transmitters. Each transmittertransmits one or more signals. Information is shared between networks.The networks together comprise a system of networks. A DVB network isidentified by a globally unique ‘network_id’. A DVB network consists ofone or more Transport Streams (TSs), each carrying a multiplex and beingtransmitted through one or more DVB signals. Information about a DVBnetwork is available within an NIT sub_table, which is identified by thenetwork_id. The NIT lists all multiplexes and DVB signals availablewithin the DVB network. The NIT is carried within each TS of the DVBnetwork.

A multiplex is a set of one or more DVB services multiplexed together,and carried on a TS. A TS carries one and only one multiplex. Amultiplex and the TS carrying it are identified by transport_stream_idand original_network_id. Transport_stream_id is unique withinoriginal_network_id. Original_network_id is the network_id of the DVBnetwork generating the multiplex.

If one multiplex is transmitted on two different DVB signals within aDVB network, the DVB signals carry the same TS. However, if the DVBsignals belong to different DVB networks, the TS is different. In bothcases, the set of DVB services, PSI information and multiplexidentifiers (transport_stream_id and original_network_id) are identical.However, if the DVB signals belong to different DVB networks, SIinformation (particularly the information about the actual DVB network,i.e. content of sections for the actual network, NIT_actual) isdifferent. In such a case, there is only one multiplex, although it iscarried on two different TSs.

Therefore, a multiplex can be considered as a set of DVB services, whilea TS can be considered as a bitstream carrying a multiplex and relatedPSI/SI information. A multiplex may be delivered on multiple DVBnetworks, while a TS belongs to only one DVB network. The network_id ofthe DVB network transmitting the TS is announced in the NIT_actualcarried within the TS.

Within a DVB network, a TS may be carried on multiple DVB signals. A DVBsignal using non-hierarchical modulation carries one TS, while a DVBsignal using hierarchical modulation carries two TSs.

It is technically possible for two networks to share the same physicaltransmitter, although this is unlikely. However, the transmitters of twonetworks can be at the same physical location, i.e. have the same cellcentre. Two or more transmitters of the same network may be at the samelocation, thus providing completely overlapping coverage resulting in asingle cell. Different transmitters can have the same or different cellsizes. Two or more transmitters of a network can form adjacent cells ifthe transmitters are not at the same location. Signals are transmittedas part of the same network if they share same network_id, which isidentified and announced in NIT.

What constitutes an available network is a matter for the networkoperator. At one extreme, an available network can be one which istransmitted by a transmitter at the same physical location as thetransmitter of the prevailing network and which has the same cell size.However, an available network can instead be available or exist withinsome specified or unspecified distance from the signal of the prevailingnetwork. Thus, an available network may relate to an adjacent or remotecell. Whether the network actually is available or not depends on thereceiver, and in particular its ability to receive a signal from atransmitter of the other network. This depends on the receiver and ongeographical factors as well as transmission power and the distancebetween the transmitter and the receiver.

In this example, a network will be considered by the system as an‘available network’ if it is broadcasting signals which may be availableto the receiver. This allows a receiver to identify what networks it maybe able to receive from one network's signal, although it does notnecessarily mean that the receiver will be able to receive all the othernetworks for the entire coverage area of the one network.

In this first embodiment, the TPS data generated by the TPS generator 16includes one TPS bit which signals the availability of other DVB-Hnetworks. Signalling is as shown in Table 2. TABLE 2 Bit n Availabilityof other DVB-H network 0 Other DVB-H networks are available 1 No otherDVB-H networks are available

The bit n can be any on of the TPS bits which currently are reserved forfuture use. However, this information can be transmitted instead usingtwo or more bits, with additional information content if required.

The syntax for the other_network_descriptor, located for example in theNIT or the BAT of the signal, is as shown in Table 3. TABLE 3 No. ofSyntax bits Identifier descriptor_tag 8 uimsbf descriptor_length 8uimsbf for (I=0; I<N; I++){ network_type 8 uimsbf network_id 16 uimsbffor (i=0; i<N; i++) { ISO_639_language_code 24 uimsbfnetwork_name_length 8 uimsbf for (j=0; j<N; j++){ char 8 uimsbf } 16uimsbf } reserved for future use 4 uimsbf signal_loop_length 12 uimsbffor (i=0; i<N; i++) { transport_stream_id 16 uimsbf original_network_id16 uimsbf frequency 32 uimsbf cell_id 16 uimsbf } }

This table loops once for each other network.

Semantics for the fields of the other_network_descriptor are as follows.

An 8-bit field ‘network_type’ identifies the type of the network thatthe descriptor relates to. This may indicate for example a DVB-Hnetwork.

A 16-bit field ‘network_id’ identifies the terrestrial network thatsupports the service indicated. This may identify for example a BBCnetwork.

‘ISO_(—)639_language_code’ is a 24-bit field which contains the ISO639-2 three character language code of the language of the network. InDVB, either ISO 639-2/B or ISO 639-2/T may be used. Each character iscoded into 8 bits according to ISO/IEC 8859-1 and inserted in order intothe field. For example, the French language has the 3-character code“fre”, which is coded as “0110 0110 0111 0010 0110 0101”.

An 8-bit field ‘network_name_length’ specifies the length in bytes ofthe network name, which is included in the following field. The‘network_name_length’ field allows a receiver to delimit the networkname bits from the other bits. The length is given as j bytes in Table3.

The ‘network_name’ field has a length determined by the‘network_name_length’ field. Each byte of the ‘network_name’ fieldconstitutes a character. This is indicated by ‘char’ (i.e. character) inTable 3. In Table 3, there are j characters. Text information is codedusing the character sets and methods described in Annex A of standard EN300 468. The field allows a receiver to determine the name of thenetwork, for example Digita.

‘ISO_(—)639_language_code’, ‘network_name_length’ and ‘network_name’fields are repeated for each available network.

Four bits of the other_network_descriptor are reserved for future use.

‘signal_looplength’ is a 12-bit field which specifies the total lengthin bytes of the signal identifying parameters that follow the field.

‘transport_stream_id’ is a 16-bit field which serves as a label foridentification of the transport stream (TS) from the equivalent network.‘original_network_id’ is a 16-bit field that gives the label identifyingthe network identification of the originating delivery system. Thedelivery system is the system where the TS was generated.

‘frequency’ is a 32 bit field which identifies the frequency at whichthe network signal is broadcast.

Finally, ‘cell_id’ is a 16-bit field which uniquely identifies the cellcarrying the network signal.

These latter four fields are repeated for each available network.

Other information or parameters may be included in the descriptor.

The parameters and other information signalled in theother_network_descriptor may be used by a receiver in the manner shownin FIG. 4 as follows.

Referring to FIG. 4, the procedure is started at step S1. At step S2 avariable “frequency” is set to the lowest frequency of the frequencyband, which in this example is 474 MHz, and a variable “f” is set to avalue of 0. At step S3 the receiver 22 is tuned to a frequency equal to“frequency” plus “f”. At step S4, it is determined by the CPU 20 whetheror not tuning lock is achieved. The absence of a tuning lock is used toinfer that no signal of sufficient strength is being transmitted at thatfrequency. Accordingly, a negative determination to step S4 leads tostep S5 where it is determined if the sum of the variables “frequency”and “f” is equal to 858 MHz, which is the highest frequency of thefrequency band in this example. If a positive determination is made, itis inferred that the entire frequency band has been searched and theprocedure proceeds to exit at step S6. Otherwise, the procedure advancesto step S7, where the variable “f” is increased by 8 MHz and theprocedure returns again to step S3. 8 MHz is the bandwidth used inFinland and other European countries, although DVB also allowsbandwidths of 6 or 7 MHz and a bandwidth of 5 MHz has also beenproposed. The bandwidth may be derived from theterrestrial_delivery_system_descriptor field of a first-decoded NIT, ormay be otherwise known by the IRD 6.

When at step S4 tuning lock is achieved, the operation proceeds to stepS8, where the TPS data is examined by the CPU 20. If the examination ofthe TPS data reveals that the network is a DVB-H network, the procedureadvances to step S9. Otherwise, it is inferred that the signal does notemanate from a suitable network type (i.e. is not a DVB-H networksignal) and the procedure retreats to step S5. Whether the network is aDVB-H network can be determined instead from the NIT for the signal, andin particular from the terrestrial_delivery system_descriptor fieldthereof. At step S9, the CPU 20 determines from the decoded TPS data,and in particular the bit thereof shown in Table 2, whether or not thereare other available networks. If the relevant TPS bit is ‘1’, revealingthat there are other available networks, an appropriate flag is set atstep S10. The number of available network signals can be determined inthis example by counting the number of networks identified in theother_network_descriptor. The number of signals can be instead becommunicated through data included in the TPS bits, as in the secondembodiment described below, or in any other suitable way. However, thenumber of other available networks does not necessarily need to bedetermined, but the receiver may choose to scan the whole band as theinformation on the number of networks is not necessarily complete. Afterstep S10, or if the TPS data indicates no other available networks, theprocedure advances to step S11.

At step S11, the PSI/SI data for the prevailing network signal isdecoded, if not already decoded, and the NIT_actual is examined. Thisexamination involves the creation of a PID (Packet IDentifier) filter(PID=0x0010) for the TS packets carrying NIT information. From thenetwork_information_sections of these packets, sections having table_id0x040 (network_information_section—actual network) are filtered forprocessing, and from these sections the network_id is stored to memory.Tuning parameters for each DVB-H signal are derived from theterrestrial_delivery descriptor. The cell_id is derived from thecell_frequency_ink_descriptor. Also, linkage information for INT table(PMT_service_id for INT) is derived for each signal from thelinkage_descriptor. Finally, time_slicing_indicator for eachtransport_stream is derived from terrestrial_delivery_system descriptor.The data relating to broadcast frequency are found in thecell_frequency_link, terrestrial delivery_system, and frequency_listdescriptors of the NIT_actual. At step S12, the NIT_actual is parsed bythe CPU 20 and the parameters needed for OSI layers 1 and 2 servicediscovery are collected therefrom. If the flag has been set at step S10to indicate the availability of other networks, theother_network_descriptor is parsed, if not already parsed, and parameterinformation concerning the other networks is collected. The relevantdata is stored in an area of temporary memory, indicated at “possiblesignals”, at step S13.

The procedure then moves onto step S14, where it is determined whetherthe flag is set. If it is, the procedure moves onto step S15, where aPID filter is created for TS packets carrying information in the NITrelating to other networks. The sections relating to other networks havetable_id of 0x41. Such sections have the same network_id as an NIT_othersub_table. The NIT_other sub-tables are then parsed at step S16, andparameters needed for OSI layers 1 and 2 service discovery are collectedfrom it. The relevant data is stored in the area of temporary memoryindicated at “possible signals” and used by step S13, at step S17. Theseare termed ‘possible signals’ since they are not necessarily known to bereceivable by the receiver 6.

At step S18 it is determined whether all the sub-tables have been parsedfor parameters. If not, then the procedure increments the sub-table atstep S19 before proceeding again to step S15. Step S18 can be carriedout in any suitable manner, for example through suitable examination ofthe section_number and last_section_number fields, or using a timeout,of 10 seconds for example.

Step S15 may implement its function by filtering only by table_id, withnetwork_id and version number being masked. A next, or unparsed,sub-table is identified through the table_id. At step S16, thenetwork_id and version number for the parsed sub-table is checked. Thenext time step S15 is carried out for that NIT_other table, thealready-parsed sub-tables are masked, to filter them out.

If step S14 determines that the flag is not set, the procedure advancesto step S20, where it is determined if all the existing signals, asidentified in other_network_descriptor, have been found. If so, signalscan is terminated at step S6. Otherwise, signal scan is continued atstep S5.

When step S18 determines that all the sub-tables for the other networkshave been parsed, the flag is cleared at step S21 before the procedureadvances to step S20.

As will be appreciated, the procedure illustrated in FIG. 4 can allowfor the identification of parameters relating to other networks, thusallowing those networks to be tuned to, without the receiving anddecoding of the NIT from the PSI/SI data for the other networks. Also,if there are no other networks, this is known from examination of theTPS bits of the one network signal, avoiding the need to scan the otherpossible frequencies at which signals may be found. This can allow thecreation of a list of possible signals utilising fewer resources and ina shorter period of time than can be achieved using the conventionalsignal scan procedure.

Since the other_network_descriptor is included in the NIT_actual,information about other networks can be gleaned earlier than in theprior art. Thus, with the first embodiment, information from othernetworks can be parsed by a receiver substantially simultaneously withthe information from the current network, at step S12 in the Figure.Accordingly, power consumption is decreased considerably, and the userexperience thereby is improved. Also, the inventors consider that theinclusion of the other_network_descriptor in the NIT_actual may allowdescriptors previously present elsewhere to be omitted altogether,allowing the size of the NIT to be reduced. This could have the effectof reducing the amount of time that an IRD needs to be switched on for,resulting in reduced power consumption.

In the example shown in FIG. 4, an entire signal scan is performed,since this can allow networks to be found even if their presence is notnotified by other networks. However, if other network signalling istreated as trustworthy, then this can be avoided.

If an entire signal scan is not required, it may still be desirable totune to the signals of the networks identified by the NIT_other table.This can be the case when for example the NIT_other sub-tables do notcontain all the information that the receiver requires.

A second embodiment will now be described, with reference to FIGS. 1 to3 and 5. Briefly, this embodiment can provide more rapid discovery ofother networks, and utilises NIT_other tables, i.e. collections ofsections describing the other networks, to carry transmission parametersrelating to other networks. NIT_other tables are known in the prior art,but this embodiment provides as additional contribution to the art. Theavailability of other networks is signalled within TPS bits, and thenumber of available other networks also is signalled within the TPSbits. The bits used for this signalling are some which currently in thestandard are reserved for future use. A receiver is able to detect theavailability and number of other networks via TPS bits. If transmissionof NIT_other is supported by the network, which it is in the embodiment,the receiver can collect transmission parameters relating to othernetworks from one or more NIT_other tables included in a first networksignal, i.e. without decoding data from those other networks. Also, whenanalysis of data from one network reveals that no other networks exist,the receiver can terminate signal scan, since further scanning would besuperfluous. Power consumption thus can be decreased considerably, anduser experience thus can be improved. The second embodiment can decreasepower consumption during signal scanning on initialisation, although itcan also be used to advantage on any signal scan, including oneperformed for the purpose of enabling handover.

A receiver is unable to detect the availability of other networks exceptby creating a filter and waiting to see if sections having table_id of0x41 (i.e. relating to NIT_other) are found. These sections formsub-tables, each sub-table including information relating to a differentnetwork. Each sub-table has the same table_id, network_id and versionnumber.

There are two table ids used for NIT sections, 0x40 for sectionsdescribing the actual network and 0x41 for sections describing othernetworks.

The structure and semantics of an NIT section describing other networkis similar to an NIT section describing the actual network. The maindifference between these is that, whereas NIT_actual (sectionsdescribing the actual network) describes the network that the current(prevailing) signal is part of, NIT_other (sections describing othernetworks) describes other existing networks which the current signal isnot part of.

In the second embodiment, the TPS data generated by the TPS generator 16includes bits as shown in Table 4. TABLE 4 Bits l, m, n No. of otheravailable DVB-H networks 000 One 001 Two 010 Three 011 Four 100 Five 101Six 110 Seven 111 Zero

Thus, bits 1, m and n of the TPS data describe exactly a number ofavailable other networks between zero and seven. The number of bits usedcould be increased or decreased if the maximum possible number ofavailable networks requires or allows this, but the inventors considerthat three TPS bits is particularly suitable for use in identifying thenumber of DVB-H networks in most circumstances.

Alternatively, the three bits TPS bits 1, m, n may instead represent thenumber of up to seven other networks with ‘000’ indicating that thereare no other networks available, and ‘ 111’ indicating that seven othernetworks are available.

Furthermore, instead of identifying precisely how many other networksare available, the TPS bits may instead together uniquely identify arange into which the number of networks falls. For example, ‘00’ mayindicate 0 or 1 other networks, ‘01’ indicates 2-4 other networks, ‘10’indicates 5-8 other networks, and so on. However, this has thedisadvantage that a receiver would not be able to determine from the TPSbits the exact number of available other networks. When the exact numberof other available networks is signalled, it can be used as counterstart or end value.

Each network transmits information relating to the physical organisationof the multiplexes/TSs carried via the network in an NIT tabledescribing the contents of the actual delivery system, and may alsocarry information describing the contents of the other delivery systemsas is known from the DVB standard ETSI EN 300 468.

For initializing the receiver 6, the following parameters may besignificant:

A 16-bit field ‘network_id’ identifies the terrestrial network thatsupports the service indicated. This may identify for example a Digitanetwork.

The ‘network_name’ field has a length determined by the‘network_name_length’ field. Each byte of the ‘network_name’ fieldconstitutes a character. This is indicated by ‘char’ (i.e. character) inTable 3. In Table 3, there are j characters. Text information is codedusing the character sets and methods described in Annex A of standard EN300 468. The field allows a receiver to determine the name of thenetwork, for example BBC.

‘transport_stream_id’ is a 16-bit field which serves as a label foridentification of the transport stream (TS) from the equivalent network.

‘original_network_id’ is a 16-bit field that gives the label identifyingthe network identification of the originating delivery system.

Finally, ‘cell_id’ is a 16-bit field which uniquely identifies the cellcarrying the network signal.

By suitable control of the transmitter stations 3-5, each networkincludes an NIT table which relates information about itself (i.e.NIT_actual) and about all of the other available networks (i.e.NIT_other). NIT other and NIT actual have similar structures, but do notnecessarily have mutually similar transmission parameter information.

Signalled parameters as described can be utilised in the receiver 6 asfollows.

Referring to FIG. 5, the procedure is started at step S1. At step S2 avariable “frequency” is set to the lowest frequency of the frequencyband, which in this example is 474 MHz, and a variable “f” is set to avalue of 0. At step S3 the receiver 22 is tuned to a frequency equal to“frequency” plus “f”. At step S4, it is determined by the CPU 20 whetheror not tuning lock is achieved. The absence of a tuning lock is used toinfer that no signal of sufficient strength is being transmitted at thatfrequency. Accordingly, a negative determination to step S4 leads tostep S5 where it is determined if the sum of the variables “frequency”and “f” is equal to 858 MHz, which is the highest frequency of thefrequency band in this example. If a positive determination is made, itis inferred that the entire frequency band has been searched and theprocedure proceeds to exit at step S6. Otherwise, the procedure advancesto step S7, where the variable “f” is increased by 8 MHz and theprocedure returns again to step S3. 8 MHz is the bandwidth used inFinland and other European countries, although DVB also allowsbandwidths of 6 or 7 MHz and a bandwidth of 5 MHz has also beenproposed. The bandwidth may be derived from theterrestrial_delivery_system_descriptor of a first-decoded NIT, and usedby the receiver to set a bandwidth parameter therein. It will beappreciated that the bandwidth must be known before the receiver 6 canlock to a signal.

When at step S4 tuning lock is achieved, the operation proceeds to stepS8, where the TPS data is examined by the CPU 20. If the examination ofthe TPS data reveals that the network is a DVB-H network, the procedureproceeds to step S9. Otherwise, it is inferred that the signal does notemanate from a suitable network type (i.e. DVB-H) and the procedureretreats to step S5. Whether the network is a DVB-H network can bedetermined instead from the NIT for the signal, and in particular fromthe terrestrial_delivery_system_descriptor thereof. At step S9, the CPU20 determines from the decoded TPS data shown in Table 4, or in avariant thereof, whether or not there are other available networks,using the number of other networks signalled. If this reveals that thereare other available networks, a count equal to the number of availablenetworks is set at step S10. Alternatively, the count can be implementedby increment. The main requirement is that it can be determined from thecount when all of the available network signals have been found. Thenumber of signals for the count is determined from the decoded TPS datashown in Table 4 or variant thereof. After step S10, or if at step S9the TPS data indicates no other available networks, the procedureadvances to step S11.

At step S11, the PSI/SI data for the prevailing network signal isdecoded, if not already decoded, and the NIT is examined. Thisexamination involves the creation of a PID (Packet IDentifier) filter(PID=0x0010) for the TS packets carrying NIT information, havingtable_id 0x40. These sections of the NIT table are filtered forprocessing, and network_id and other relevant parameters are extractedtherefrom and stored to memory. Tuning parameters for each DVB-H signalare derived from the terrestrial_delivery_descriptor. The cell_id isderived from the cell_frequency_link_descriptor. Also, linkageinformation for INT table (PMT_service_id for INT) is derived for eachsignal from the linkage_descriptor. Finally, time_slicing_indicator foreach transport_stream is derived from terrestrial_delivery systemdescriptor. The data relating to broadcast frequency are found in thecell_frequency_link, terrestrial delivery system, and frequency_listdescriptors of the NIT

At step S12, the information in the network_id field for the prevailingnetwork is examined. At step S13 it is determined from the network_idfield whether the NIT has already been parsed. The NIT will already havebeen parsed if the NIT was included in any of the previously foundsignals. If the NIT has already been parsed, the procedure advances tostep S19. If the NIT has not already been parsed, at step S14 the NIT isparsed by the CPU 20 and the parameters needed for OSI layers 1 and 2service discovery are collected therefrom. Also, the next‘network_information_section—other_network’ is processed. The relevantdata is stored in an area of temporary memory, indicated at “possiblesignals”, at step S15. The procedure then moves onto step S16, where itis determined whether the count, which was set at step S10 but which mayhave been decremented, is zero. If it is not zero, a PID filter iscreated for TS packets carrying information on NIT relating to othernetworks at step S17. The sections relating to other networks havetable_id of 0x41. Such sections having the same network_id form aNIT_other sub_table. The NIT_other sub-table is then parsed at step S18,and transmission parameter information, including parameters needed forOSI layers 1 and 2 service discovery, are collected from it. The networktransmission parameters for the other network signal are stored in thearea of temporary memory indicated at “possible signals” and used bystep S15, at step S20. These are termed ‘possible signals’ since theyare not necessarily known to be receivable by the receiver 6. Thenetwork_id for the parsed sub-table is checked also at step S18. At stepS21 the counter is decremented, and the counter for sub_table isincremented. The next time step S17 is carried out for that NIT_othertable, the already-parsed sub-tables are masked, to filter them out.

When step S16 responds with a ‘yes’ reply, since the transmissionparameters for all the other available networks have been parsed atsteps S14 and S18, these parameters are stored in the flash memory 27 atstep S22. Following step S22, at step S19, it is determined if all theexisting signals, as identified in the TPS data illustrated in Table 4or variant thereof, have been found. If so, signal scan is terminated atstep S6. Otherwise, signal scan is continued at step S5.

Optionally, the version number of the NIT table may be checked on eachfiltering so that obsolete NIT tables are not used. This would occur atsteps S14 and step S18 in FIG. 5. If the version number is the same,then it can be assumed that the NIT table is valid. If the versionnumbers are different, then it can be assumed that the NIT table is notnecessarily valid, and the table with the latest version number is givenpriority. Both NIT_actual and NIT_other table types have versionnumbers.

If the TPS data identifies that no other networks are available, thenthe procedure can be terminated following parsing of the transmissionparameters from the single network, without needing to scan for othernetworks, thereby saving time and power consumption.

As will be appreciated, the procedure illustrated in FIG. 5 can allowfor the identification of parameters relating to other networks, thusallowing those networks to be tuned to, without the receiving anddecoding of the NIT from the PSI/SI data for the other networks. Also,if there are no other networks, this is known from examination of theTPS bits of the prevailing network, avoiding the need to scan the otherpossible frequencies at which signals may be found. In this case, signalscanning can be avoided even if NIT_other is not supported by henetwork. This can allow the creation of a list of possible signalsutilising fewer resources and in a shorter period of time than can beachieved using the prior art procedure.

If the number of available other networks is signalled, the scanning canbe terminated as soon as the signalled number of other networks arefound and in such case it is not necessary to scan the whole frequencyband (in this example 474-858 MHz).

When NIT_other is used to carry transmission parameters relating toother networks, the bandwidth of the transmitted signals is increased.However, this is considered by the inventors to be acceptable in view ofthe advantages that can be experienced by receivers.

In both of the embodiments, the IRD 6 is arranged to cause to bedisplayed on the display 26, in a GUI, information allowing the user toview whether there are other networks available, and preferably also toview their number. To advantage, the IRD 6 displays information relatingto each available network. This information can simply be the networkname, or it may also be other information obtained from the NIT or otherdata. Once service discovery has been performed, the IRD 6 can displayas well data relating to one or more services forming part of thenetworks. The GUI can be controlled by the user to display theinformation that the user requires to view.

The standards that are referred to in the above embodiments are ETSI EN300 744 and ETSI EN 300 468. Although the above embodiments have beendescribed in relation to the DVB broadcast system, it will beappreciated that that the principles can be transferred to otherbroadcast systems or to multicast or unicast systems. Such a system maybe DVB-T, DVB-H, or the Advanced Television System (ATSC) or theJapanese Integrated Services Digital Broadcasting (ISDB, or ISDB-T)system, to list some non-limiting examples.

II. Handover Between Cells

In accordance with aspects of the invention, cells are modeled withbitmaps that provide real-life free field two or three dimensional planemodels of the signal levels existing in a well-defined adjustable areaand resolution. This is in contrast to conventional methods that usebulky rectangular representations of coverage areas of cell.

The aspects of the invention described herein are particularly wellsuited for use with DVB type cells. For example, embodiments introduce asignaling method, which can be used to improve mobility in DVB-T/Hnetworks i.e. determination and signaling of the coverage area of cell(size of cell and location of cell). Currently the signalinggeographical location of cell is roughly defined in DVB PSI/SIspecifications. Aspects of the invention provide a signaling method,which improves accuracy for this.

Bitmap information may be created based on the measurements within thearea of each cell. The signal strength values may be received from oneor more terminals or testing devices. The received values may then beprocessed e.g. statistically and compared to values provided by othermeans such as from dedicated measurement devices, which may be mobile orfixed. The bitmap is not restricted to using elementary cells, which aresquare-shaped. The cells may take a variety of different forms, such astriangle, preferably equilateral, or a hexagon, which may be composed ofsix equilateral triangles. One or more bitmaps may also be in a form ofconcentric circles or circular zones, wherein each of the ‘belts’ may bedivided into segments.

Two or more neighboring cells may be combined to one cell for which thesignal strength is announced. In these cases, the addressing of thecells may be adapted to suit the selected elementary cell shape. Also a‘reference point’ of the bitmap expressed in the exemplary embodimentwith latitude and longitude coordinates may be chosen otherwise e.g. asa center point of the cell or as the location of the transmittingantenna.

FIG. 6 illustrates the mapping of signal coverage area into a bitmap, inaccordance with an embodiment of the invention. A transmission tower 600transmits a signal within a coverage area defined by circle 602, whichfits within square area 604. A bitmap 606 includes a grid thatrepresents signal strengths. For example, an area 608 represents pointsthat have a first signal strength and are represented by a first shadeand an area 610 represents points that have a second signal strength andare represented by a second shade. Of course, the granularity of bitmap606 may be increased to represent numerous additional levels of signalstrength.

Bitmaps may also represent non-uniform field patterns. FIG. 7illustrates the mapping of a non-uniform signal coverage area into abitmap, in accordance with an embodiment of the invention. Transmitter702 produces a field pattern 704 that results in a bitmap 706 havingsignal strength levels 708 and 710. Transmitter 712 produces a fieldpattern 714 that results in a bitmap 716 having signal strength levels718 and 720.

Bitmap information may be provided as an input to any signalling item(such as a cell descriptor table), which provides bitmap information tomobile terminals. In some embodiments of the invention bitmaps may beavailable in more than one version. The version may have differentdegrees of detail and differ from each other e.g. with regard toelementary cell size and/or depth. The different versions may besignaled to a mobile terminal so that the terminal may select which ofthe versions it receives and stores. In one embodiment of the invention,the order of the versions may be such that the first map(s) are not asdetailed as the later ones with regard to the elementary cells sizeand/or depth. The bitmap, parts of it, its IP address or itsavailability may be sent to a mobile terminal in some embodiments of theinvention by using SMS or MMS as some terminals may have thefunctionality of a mobile phone and a DVB receiver. The same informationmay be sent over other communications networks.

FIG. 8 illustrates an exemplary method for generating bitmaps, inaccordance with an embodiment of the invention. First, in step 802measurements of the free field signal strengths of one or more cells isperformed. Step 802 may be performed by using a testing device tomeasure actual signal strengths within a cell. Step 802 may be performedperiodically or when a cell is modified in a manner that may impact thesignal strengths. In an alternative embodiment, a model of a cell may beused to estimate free field signal strengths within a cell. In step 804,the measured or estimated values are transformed into bitmaps describingcell coverage areas. One skilled in the art will appreciate that thereare numerous methods that may be used to transform one or more lists ofsingle strength values into a bitmap. A detailed example is providedbelow. Next, a signaling item is generated in step 806. In exemplaryembodiments the signaling item is in the form of a cell descriptor tableor OSI layer 3-7 item. Finally, in step 808 the generated item istransmitted to a mobile terminal.

FIG. 9 illustrates an exemplary method for parsing and utilizing asignaling item containing bitmap information in accordance with anembodiment of the invention. First, in step 902 the signalinginformation is received and parsed. The signaling item may be in theform of a DVB-H/T signal that includes a cell descriptor table that willbe parsed. Next, a map of the cell may be generated according to thebitmap information in step 904. The availability of signals based on thebitmap information is determined in step 906. Step 906 may includedetermining which cells have a predetermined signal strength over apredetermined geographic area. Finally, bitmap information is used toassist in handover decisions in step 908. The process shown in FIG. 9may be stored in the form of computer-executable instructions stored ona computer-readable media. A CPU within a mobile terminal may beconfigured to execute the computer-executable instructions.

FIG. 10 illustrates a system for creating a data file that containsbitmap information, in accordance with an embodiment of the invention.Input data 1002 and configuration parameters 1004 are provided to acomputing unit 1006. Input data may include measured and/or estimatedsignal strengths. Configuration parameters 1004 may include resolution,size, scale, etc. Computation unit 1006 may be implemented with acomputer device that is programmed to process input data 1002 andconfiguration parameters 1004 to create a data file 1008.

FIG. 11 illustrates a system for receiving a data file, creating aCDT-table and broadcasting the CDT-table to mobile terminals, inaccordance with an embodiment of the invention. Data file 1008 may bestored on a server 1102 and server 1102 processes data file 1008 toproduce a cell descriptor table 1104. Of course, one or more additionalor alternative devices may be used to store and process data file 1008and create cell descriptor table 1104. A multiplexer 1106 inserts celldescriptor table 1104 into a transport stream 1108. A transmissionstation 1110 may then transmit the transport stream to a mobile terminal1112.

In alternative embodiments, a bitmap can be transferred to a mobileterminal by other means. For example FileCast, or download using someother bi-directional network interface.

An exemplary structure and semantics of cell descriptor table(CDT-Table) is shown below in Table 5. TABLE 5 Cell description sectionSyntax No. of bits Identifier cell_description_section( ) { table_id 8uimsbf section_syntax_indicator 1 bslbf reserved_future_use 1 bslbfReserved 2 bslbf section_length 12 uimsbf cell_id 16 uimsbf Reserved 2bslbf version_number 5 uimsbf current_next_indicator 1 bslbfsection_number 8 uimsbf last_section_number 8 uimsbf network_id 16uimsbf if (section_number == 0){ Width 8 uimsbf Height 8 uimsbf Scale 8uimsbf lo_bound 8 uimsbf hi_bound 8 uimsbf Depth 3 uimsbf Compression 2bslbf Reserved_future_use 2 bslbf Latitude 25 uimsbf Longitude 26 uimsbfReserved_future_use 2 bslbf data_length 12 uimsbf for(i=0;i<N;i++){ Byte8 uimsbf } } for(i=0;i<N;i++){ cell_id_extension 8 uimsbf subcell_width8 uimsbf subcell_height 8 uimsbf subcell_scale 8 uimsbf subcell_lo_bound8 uimsbf subcell_hi_bound 8 uimsbf subcell_depth 3 uimsbfsubcell_compression 2 bslbf Reserved_future_use 2 bslbf subcell_latitude25 uimsbf subcell_longitude 26 uimsbf Reserved_future_use 2 bslbfsubcell_data_length 12 uimsbf for(i=0;I<N;i++){ subcell_byte 8 uimsbf }} CRC_32 32 rpchof

Semantics for the cell description section:

table_id: identifier of the table.

section_syntax_indicator: The section_syntax_indicator is a 1-bit fieldwhich shall be set to “1”.

section_length: This is a 12-bit field, the first two bits of whichshall be “00”. It specifies the number of bytes of the section, startingimmediately following the section_length field and including the CRC.The section_length shall not exceed 4093 so that the entire section hasa maximum length of 4096 bytes.

cell_id: This is a 16-bit field which uniquely identifies a cell.

version_number: This 5-bit field is the version number of the sub-table.The version_number shall be incremented by 1 when a change in theinformation carried within the sub_table occurs. When it reaches value31, it wraps around to 0. When the current_next_indicator is set to ‘1’,then the version_number shall be that of the currently applicablesub_table defined by the table_id, platform_id and action_type. When thecurrent_next_indicator is set to ‘0’, then the version_number shall bethat of the next applicable sub_table defined by the table_id,platform_id and action_type.

current_next_indicator: This 1-bit indicator, when set to ‘1’ indicatesthat the sub_table is the currently applicable sub_table. When the bitis set to ‘0’, it indicates that the sub_table sent is not yetapplicable and shall be the next sub_table to be valid.

section_number: This 8-bit field gives the number of the section. Thesection_number of the first section in the sub_table shall be “0x00”.The section_number shall be incremented by 1 with each additionalsection with the same table_id, platform_id and action_type.

last_section_number: This 8-bit field indicates the number of the lastsection (that is, the section with the highest section_number) of thesub_table of which this section is part.

network_id: This is a 16-bit field that identifies the network that thedescribed cell is part of.

width: This 8-bit field specifies the width of the bitmap in pixels.

height: This 8-bit field specifies the height of the bitmap in pixels.

scale: This 7-bit field tells the geographical size of one bitmap pixel.The size is scale* 10 m, so that e.g. 42 would specify that each pixelrepresents a geographical area of 420 m*420 m.

lo_bound: This 7-bit field is the low bound of field strength. It is theabsolute value of the dBm value represented by pixel value 1. If bitdepth is 1, this shall be the same as hi_bound.

hi_bound: This 7-bit field is the high bound of field strength. It isthe absolute value f of the dBm value represented by the highestpossible pixel value. If bit depth is 1, this shall be the same aslo_bound.

latitude: This 25-bit field tells the geographical position of thelower-left (south-west) corner of the bitmap. This field shall be set tothe two's complement value of the latitude, referenced to the WGS-84reference ellipsoid, in units of 180/2²⁵ degrees, in the range from −90degrees to +90×(1-2⁻²⁴) degrees, counting positive angles north of theequator and negative angles south of the equator.

longitude: This 26-bit field tells the geographical position of thelower-left (south-west) corner of the bitmap. This field shall be set tothe two's complement value of the longitude, referenced to the WGS-84reference ellipsoid, in units of 360/2²⁶ degrees, in the range from −180degrees to +180×(1-2⁻²⁵) degrees, counting positive angles east of theGreenwich meridian and negative angles west of the Greenwich meridian

depth: This 3-bit field is the bit depth of the bitmap. The bit depthtells how many bits are used to specify each pixel, i.e. bit depth of 4would indicate that the bitmap has 2⁴=16 levels. It shall not be 0.

compression: This 2-bit field tells the compression method used tocompress the bitmap data. Exemplary compression values are described inTable 6. TABLE 6 Signalling compression method Compression Compressionmethod 00 Uncompressed 01 Reserved for future use 10 Reserved for futureuse 11 Reserved for future use

data_length: This 12-bit field specifies the length in bytes of thefollowing bitmap data.

byte: This is an 8-bit field. An array of byte fields specify the bitstring of bitmap data compressed using the method specified incompression field. If necessary, the bit string is padded with ‘0’-bitsto meet next 8-bit boundary at the end of data.

cell_id_extension: This 8-bit field is used to identify a subcell withina cell.

subcell_width: see width.

subcell_height: see height.

subcell_scale: see scale.

subcell_lo_bound: see lo_bound.

subcell_hi_bound: see hi_bound.

subcell_latitude: see latitude.

subcell_longitude: see longitude.

subcell_depth: see depth.

subcell_compression: see compression.

subcell_data_length: see data_length.

subcell_byte: see byte.

CRC_(—)32: This is a 32-bit field that contains the CRC value that givesa zero output of the registers in the decoder defined in EN 300 468after processing the entire private section.

In alternative embodiments, other means to deliver the data file to aterminal may be used, e.g. OSI layer 3-7 signalling can be used as well.(Bitmaps could be provided e.g. as separate service or within part ofESG or similar).

FIG. 12 illustrates an exemplary data structure for expressing vectorinformation, in accordance with an embodiment of the invention. Anexemplary vector 1300 representing movement of a mobile terminal 1302relative to a cell 1304 and a cell 1306 is shown in FIG. 13. Datagram1200 comprises header information 1201 (such as the source IP addressand the destination address) and data payload 1237. Also, datagram 1200comprises geographical position information about a source devicecorresponding to a option type data field 1240, an option length datafield 1241, a reserved data field 1249, a version data field 1251, adatum data field 1253, a latitude data field 1203, a longitude datafield 1205, altitude data fields 1207 and 1239, velocity data fields1209, 1211, 1213, and 1215, location uncertainty data fields 1217, 1219,1221, 1223, and 1225, velocity uncertainty data fields 1227, 1229, 1231,and 1233, and time data field 1235. Time data field 1235 is a 40-bitfield that contains the current time and data in Coordinated UniversalTime (UTC) and Modified Julian Date (MJD). Field 1235 is coded as 16bits providing 16 LSBs of the MJD followed by 24 bits that represent 6digits in a 4-bit Binary-Coded Decimal (BCD). In the exemplaryembodiment, the geographical information is contained in a destinationoptions header or in a hop-by-hop header, in compliance with RFC 2460.In the embodiment, a destination options header and a hop-by-hop headermay be contained in the same datagram.

Referring to FIG. 12, the full width may correspond to 32 bits (4octets). However, other embodiments of the invention may utilizedifferent data field alignments and different data widths for any of thedata fields. In the exemplary embodiment, the data fields may becontained in a header that is compatible with RFC 2460.

In the exemplary embodiment, version data field 1251 is an 8-bit fieldthat indicates the version of the message header. Datum data field 1253is an 8-bit field that indicates the used map datum (e.g., standardMIL-STD-2401) for determining the geographical position. Latitude datafield 1203 is a 32-bit field that indicates the latitude value of thesource device (e.g., corresponding to an approximate location ofterminal node 107) presented in ANSI/IEEE Std 754-1985 format. Longitudedata field 1205 is a 32-bit field that indicates the longitude value ofthe source device presented in ANSI/IEEE Std 754-1985 format. Altindicator data field 1239 is a 1-bit field indicating the use ofaltitude information. Altitude data field 1207 is a 16-bit field thatindicates the altitude value of the source device presented in ANSI/IEEEStd 754-1985 format.

Velocity indicator data field 1209 is a 1-bit field indicating the useof velocity information. If velocity information is included, this fieldis set to ‘1’. Otherwise this field is set to ‘0’. Heading data field1211 is a 16-bit field that indicates the direction where the mobilenode is moving. If velocity indicator data field 1209 is set to ‘0’,this field is ignored. Otherwise, this field is included and is set tothe angle of axis of horizontal velocity uncertainty, in units of 5.625degrees, in the range from 0 to 84,375 degrees, where 0 degrees is TrueNorth and the angle increases toward the East. Vertical velocity datafield 1213 is an 8-bit field, which indicates the vertical velocity ofthe mobile node. Vertical velocity data field 1213 is used if field 1209is set to ‘1’. Horizontal velocity data field 1215 is a 16-bit fieldthat indicates the horizontal velocity of the mobile node. If velocityindicator is set to ‘1’, this field is in use. Once used, the horizontalspeed is set in units of 0.25 m/s, in the range from 0 to 511.75 m/s.Otherwise this field is ignored.

Loc_Unc_H indicator data field 1217 is a 1-bit field which indicates thehorizontal position uncertainty, including elliptical. If ellipticalhorizontal position uncertainty information is included in this responseelement, this field is set to ‘1’. Otherwise, this field is set to ‘0’.Loc_Unc angle data field 1219 (angle of axis of the standard errorellipse for horizontal position uncertainty) is an 8-bit fieldindicating the angle of axis of the standard error ellipse forhorizontal position uncertainty. If Loc_Unc_H indicator field 1217 isset to ‘0’, this field is ignored. Otherwise, this field is included andis set to angle of axis for horizontal position uncertainty, in units of5.625 degrees, in the range from 0 to 84.375 degrees, where 0 degrees isTrue North and the angle increases toward the East. Loc_Unc A data field1221 (standard deviation of error along angle specified for horizontalposition uncertainty) is an 8-bit field indicating the standarddeviation of error along angle specified for horizontal positionuncertainty. If Loc_Unc A data field 1221 is set to ‘0’, this field isignored. Otherwise, this field is included and is set to represent thestandard deviation of the horizontal position error along the axiscorresponding to Loc_Unc angle data field 1219. Loc_Unc P data field1223 (standard deviation of error along angle specified for horizontalposition uncertainty) is a 8-bit field indicating standard deviation oferror along angle specified for horizontal position uncertainty. IfLoc_Unc P data field 1223 is set to ‘0’, this field is ignored.Otherwise, this field is included and is set to represent the standarddeviation of the horizontal position error perpendicular to the axiscorresponding to Loc_Unc angle data field 1219. Loc_Unc vertical datafield 1225 (standard deviation of vertical error for positionuncertainty) is an 8-bit field indicating standard deviation of verticalerror for position uncertainty.

Vel_Unc angle data field 1227 (angle of axis of standard error ellipsefor horizontal velocity uncertainty) is an 8-bit field indicating theangle of axis of standard error ellipse for horizontal velocityuncertainty. If Vel_Unc angle data field 1227 is set to ‘0’, this fieldis ignored. Otherwise, this field is set to the angle of axis forhorizontal velocity uncertainty, in units of 5.625 degrees, in the rangefrom 0 to 84,375 degrees, where 0 degrees is True North and the angleincreases toward the East. Vel_Unc A data field 1229 (standard deviationof error along angle specified for horizontal velocity uncertainty) isan 8-bit field indicating standard deviation of error along anglespecified for horizontal velocity uncertainty. If velocity indicatordata field 1209 is set to ‘1’, this field is included and is set torepresent the standard deviation of the horizontal velocity error alongthe angle corresponding to Vel_Unc angle data field 1227. Vel_Unc P datafield 1231 (standard deviation of error perpendicular to angle specifiedfor horizontal velocity uncertainty) is a 8-bit field indicatingstandard deviation of error perpendicular to angle specified forhorizontal velocity uncertainty. If velocity indicator data field 1209is set to ‘1’, this field is included and is set to represent thestandard deviation of the horizontal velocity error perpendicular to theangle corresponding to Vel_Unc angle data field 1227. Otherwise, thisfield is ignored. Vel_Unc vertical data field 1233 (standard deviationof vertical velocity error) is an 8-bit field indicating the standarddeviation of vertical velocity error.

In the embodiment shown in FIG. 12, location uncertainty data fields1219-1225 may be used to define a geographical area, where the data oflocation uncertainty data fields may not be as specified by standards,but can be used by an application for conveying region information. Insuch a case, the application could recognize the use of locationuncertainty data fields 1219-1225 and/or the variation from thespecification as indicated in some other field of the header.

One skilled in the art will appreciate that the network handover andcell handover aspects of the invention may be combined and usedtogether. For example, FIG. 14 illustrates an exemplary method forexecuting a handover decision between networks and cells, in accordancewith an embodiment of the invention.

In step 1402 it is determined whether or not a DVB-H network isavailable. When a network is available, in step 1404 it is determinedwhether or not an NIT update is needed. When an NIT update is needed, instep 1414 NIT tables are collected for actual delivery systems and otherdelivery systems. The delivery systems in step 1414 may be DVB-Hnetworks. When it is determined that a DVB-H network is not available instep 1402, in step 1406 a mobile terminal seeks DVB-H networks.Conventional network seeking methods may be used in step 1406.

In step 1408 it is determined whether or not a DVB-H network has beenfound. When such a network has been found, control passes to step 1414.When a DVB-H network has been found, an indication may be displayed to auser of a mobile terminal in step 1410. For example, an indicationindicating that no DVB-H networks are available may be displayed. Next,a user may determine whether or not the user wishes for the mobileterminal to continue seeking DVB-H networks in step 1412. When the userdecides not to continue seeking DVB-H networks, the process ends. Whenthe user desires for the mobile terminal to continue seeking DVB-Hnetworks, control returns to step 1406.

After step 1414 or when an NIT update is not needed, it is nextdetermined whether or not an INT update is needed in step 1416. Whensuch an update is needed, an INT information update operation isperformed in step 1418. After step 1418 or when an INT update is notneeded, it is next determined whether a cell coverage information updateis needed in step 1420. When such an update is needed, an operation forcollecting cell descriptor tables for the current and adjacent cells isperformed in step 1422.

After step 1422 or when no cell coverage information update is needed,it is next determined whether or not position update information isneeded in step 1424. When such an update is needed, an operation isperformed for updating the geographic position of the mobile terminal instep 1426. Step 1426 may include using a global positioning systemmodule or any other conventional method for determining the position ofa mobile terminal. After step 1426 or when position update informationis not needed, a mobile terminal then iterates through handovercandidates in step 1428. One skilled in the art will appreciate thatnumerous methods may be used to select the best handover candidate withthe information that has been obtained by executing the process shown inFIG. 14. After handover candidates have been examined, in step 1430 themobile terminal executes a handover operation between networks and/orcells.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

1. A method of operating a receiver, the method comprising: (a)receiving a signal digitally broadcast from a transmitter of aprevailing network, the signal including transmission parameterinformation bits; (b) decoding the transmission parameter informationbits from the received signal; and (c) determining from the decodedtransmission parameter information whether or not one or more othernetworks are available.
 2. The method as claimed in claim 1, wherein (c)comprises determining from the decoded transmission parameterinformation bits the number of other networks that the digital broadcastincludes.
 3. The method as claimed in claim 1, wherein (b) comprisesdecoding a network information table from the signal, and determiningfrom the decoded network information table transmission parameters ofone or more of the other networks.
 4. The method as claimed in claim 3,further comprising using the transmission parameters to tune thereceiver to the one or more other signals.
 5. The method as claimed inclaim 1, further comprising: scanning for signals from the one or moreother networks, determining from the decoded transmission parameterinformation whether any of the other networks remain unfound, andceasing scanning when the number of unfound networks is determined to bezero.
 6. The method as claimed in claim 1, wherein (b) comprises:decoding other network descriptor information from the received signal,to identify the number of other networks.
 7. The method as claimed inclaim 2, further comprising: scanning for signals from the one or moreother networks, determining from the number of networks whether any ofthe other networks remain unfound, and ceasing scanning when the numberof unfound networks is determined to be zero.
 8. The method as claimedin claim 1, further comprising: obtaining from the decoded other networkdescriptor information transmission parameters relating to the one ormore other networks.
 9. The method as claimed in claim 1, furthercomprising: decoding other network descriptor information from thenetwork, to obtain transmission parameters relating to other networks.10. The method as claimed in claim 9, further comprising using thetransmission parameters to tune the receiver to one or more othersignals.
 11. The method as claimed in claim 10, in which the parametersinclude tuning information.
 12. A method of operating a receiver, themethod comprising: (a) receiving a signal digitally broadcast from atransmitter of a prevailing network, the signal including other networkdescriptor information; (b) decoding the other network descriptorinformation from the received signal, (c) obtaining from the othernetwork descriptor information transmission parameters relating to oneor more other networks, and (d) using the transmission parameters totune the receiver to the one or more other networks.
 13. The method asclaimed in claim 12, wherein the transmission parameters include tuninginformation.
 14. A receiver comprising: a receiver module arranged forreceiving a signal digitally broadcast from a transmitter of aprevailing network, the signal including transmission parameterinformation bits; a decoder for decoding the transmission parameterinformation from the received signal; and a determiner for determiningfrom the decoded transmission parameter information whether or not othernetworks are available.
 15. A receiver comprising: a receiver modulearranged for receiving a signal digitally broadcast from a transmitterof a prevailing network, the signal including other network descriptorinformation; a decoder for decoding the other network descriptorinformation from the received signal, means for obtaining from thedecoded other network descriptor information transmission parametersrelating to one or more other networks, and a tuner controller arrangedfor using the transmission parameters relating to the one or more othernetworks to tune the receiver module to the one or more other networks.16. The receiver as claimed in claim 15, further including a displayconfigured to display data relating to other networks.
 17. A method offorming a signal for digital broadcast by a transmitter of a network,the method comprising: creating transmission parameter informationincluding an indication of whether or not other networks are availablewithin the broadcast.
 18. The method as claimed in claim 17, wherein thecreating step comprises including an indication of the number of othernetworks that the digital broadcast includes.
 19. The method as claimedin claim 18, wherein the creating step comprises including an indicationof the number of other networks that the digital broadcast includes inother network descriptor information.
 20. The method as claimed in claim19, wherein the creating step comprises including transmissionparameters relating to other networks in other network descriptorinformation.
 21. The method as claimed in claim 20, comprising formingthe signal by creating a network information table, the networkinformation table including transmission parameters of one or more ofthe other networks.
 22. A method of forming a signal for transmission bya transmitter of a network, the method comprising: creating othernetwork descriptor information for a network of a digital broadcast, andincluding in the other network descriptor information transmissionparameters identifying whether or not other networks are available inthe digital broadcast.
 23. A transmission parameter signalling datasignal for broadcast by a transmitter of a network, the signalcomprising a predetermined number of data bits defined over consecutiveorthogonal frequency division multiplex symbols, the data signalcomprising at a predetermined location a group of one or moreinformation bits having a state dependent on whether or not othernetworks are available.
 24. A method of operating a mobile terminal, themethod comprising: receiving cell data from a transmission site within afirst cell; and extracting from the cell data a plurality of quantizedsignal levels for at least a second cell and a third cell that are bothadjacent to the first cell; and performing a handover operation based onthe plurality of quantized signal levels.
 25. The method of claim 24,wherein the plurality of quantized signal levels are in the form of acell description table.
 26. The method of claim 24, wherein theplurality of quantized signal levels represent free field threedimensional models of signal levels.
 27. The method of claim 24, whereinthe plurality of quantized signal levels are in the form of bitmaps. 28.A receiver comprising: a receiver module that receives cell data from atransmission site within a first cell; and a processor configured toperform the steps comprising: extracting from the cell data a pluralityof quantized signal levels for at least a second cell and a third cellthat are both adjacent to the first cell; and performing a handoveroperation based on the plurality of quantized signal levels.
 29. Thereceiver of claim 28, wherein the plurality of quantized signal levelsare in the form of a cell description table.
 30. The receiver of claim28, wherein the plurality of quantized signal levels represent freefield three dimensional models of signal levels.
 31. The receiver ofclaim 28, wherein the plurality of quantized signal levels are in theform of bitmaps.
 32. A method of forming a signal for transmission by atransmitter of a network, the method comprising: creating a celldescription table containing a plurality of quantized signal levels forcell for a mobile communications network.
 33. The method of claim 32,wherein the plurality of quantized signal levels are in the form of abitmap.